Abstract

Rigidity sensing plays a fundamental role in multiple cell functions ranging from migration, to proliferation and differentiation (Engler et al., Cell 126:677–689, 2006; Lo et al., Biophys. J. 79:144–152, 2000; Wells, Hepatology 47:1394–1400, 2008; Zoldan et al., Biomaterials 32:9612–9621, 2011). During migration, single cells have been reported to preferentially move toward more rigid regions of a substrate in a process termed durotaxis. Durotaxis could contribute to cell migration in wound healing and gastrulation, where local gradients in tissue rigidity have been described. Despite the potential importance of this phenomenon to physiology and disease, it remains unclear how rigidity guides these behaviors and the underlying cellular and molecular mechanisms. To investigate the functional role of subcellular distribution and dynamics of cellular traction forces during durotaxis, we developed a unique microfabrication strategy to generate elastomeric micropost arrays patterned with regions exhibiting two different rigidities juxtaposed next to each other. After initial cell attachment on the rigidity boundary of the micropost array, NIH 3T3 fibroblasts were observed to preferentially migrate toward the rigid region of the micropost array, indicative of durotaxis. Additionally, cells bridging two rigidities across the rigidity boundary on the micropost array developed stronger traction forces on the more rigid side of the substrate indistinguishable from forces generated by cells exclusively seeded on rigid regions of the micropost array. Together, our results highlighted the utility of step-rigidity micropost arrays to investigate the functional role of traction forces in rigidity sensing and durotaxis, suggesting that cells could sense substrate rigidity locally to induce an asymmetrical intracellular traction force distribution to contribute to durotaxis.

Notes

Acknowledgments

We acknowledge financial support from the National Institutes of Health (EB00262, HL73305, and GM74048), the Penn Institute for Regenerative Medicine, the Nano/Bio Interface Center, and the Center for Musculoskeletal Disorders of the University of Pennsylvania. J. F. was partially funded by the American Heart Association Postdoctoral Fellowship, and R. D. was supported by a National Science Foundation Fellowship. We thank Pan Mao for assistance in scanning electron microscopy. The M.I.T. Microsystems Technology Laboratories is acknowledged for support in cleanroom fabrication.